Automatic pilot



G. W. RUSLER AUTOMATIC PILOT April 7, 1953 2 SHEETS--SHEET 2 Filed July23, 1948 SERVO Patented Apr. 7, 1953 AUTOMATIC PILOT George W. Rusler,Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company,Minneapolis, Minn., a corporation of Delaware Application July 23,1948,Serial No. 40,312

(Cl. S18-489) 17 Claims.

This invention pertains to automatic steering mechanisms for dirigiblecraft of the type commonly known as automatic pilots for aircraft. Thisinvention is more particularly concerned with an interlockingarrangement for an automatic pilot.

An aircraft provided with an automatic pilot has control surfaces whichgenerally may be alternatively controlled by the automatic pilot or bydirect manual operation.

`One form ci automatic pilot is provided with power means which may beplaced in association with the control surfaces to operate them. Thepower means is controlled by electrical signal deriving devices whichare connected to a source of supply voltage. The signal devices areoperated by stabilizing means which stabilizing means thus control thepower means to operate the control surfaces to thereby maintain theaircraft in a desired position. The association of the power means withthe control surfaces is manually controlled.

It is an object of this invention to automatically disassociate saidpower means from said control surfaces upon failure of voltage supply tosaid signal devices and to prevent such future association until saidsupply is reestahlished.

The stabilizing means for operating one such signal device may comprisea gyroscope whose rotor is maintained automatically in a desiredposition. The rotor generally is not initially at this desired positionbut must be processed to this position. it is a further object of thisinvention to provide an interlock arrangement whereby a rapid initialprocession provided,-

resulting in the approach to said position by the rotor. This rapidprocession is obtained during less than normal rotational speed of therotor with the rotor thereafter being permitted to attain fullrotational speed all before the association of said power means and saidcontrol surfaces inay be effected.

It is a further object of this invention to provide a balanceablecontrol system for controllingr a servomotor including means forbalancing said system while said motor is not being utilized andcomprising interlock means whose operation is initiated with theconnection of said system to a source of voltage to provide a period oftime for i'ebalancing said system before said servomotor may beutilized.

It is a further object of this invention to provide such balanceablecontrol system with signal providing elements responsive to changes indirection and attitude and with interlock means to prevent associationof said system with said servomotor until the elements of said systemhave had a period to approach a desired normal balanced position.

These and further objects of this invention will become apparent from aconsideration of the following description taken in connection with theaccompanying drawings wherein: Figures 1A and 1B together illustrateapparatus for controlling one control surface of an aircraft.

'The type of automatic pilot to which this invention has been appliedmay control the aircraft about the vertical axis, the roll axis, and thepitch axis. For the purpose of simplifying the disclosure, the inventionis illustrated as it is applied to the rudder control of the automaticpilot. The yextension to the aileron control as well as the elevatorcontrol will be apparent as the description proceeds.

Figure 1B of the drawing illustrates an arrangement for controlling therudder of the aircraft. The rudder (not shown) which controls theaircraft about its vertical axis is operated by cables lil extendingfrom a cable drum il carried by a shaft l2 which is driven by aservornotor i3. The servomotor i3 is reversibly controlled by an amplierI4 through a rudder relay iii to be described. The amplier servomotorcombination may be of the type disclosed in the application of Willis H.Gille, Serial Number 447,989.

Amplifier M is provided with leads l1, I8 connected to a source ofalternating voltage such as the ships supply. The amplifier I4 is alsoprovided with signal input connections IS, and 20 which are connected toa signal circuit to be described. The direction of rotation ofservomotor is depends upon the phase relationship between the voltageapplied across the power input leads l'i, 18 and that applied across thesignal input connections i9, 2S. rihe signal input circuit extends fromconnection IS, network 22, lead td, network 4t, lead S6, network 52,lead 14 to ground and to the grounded lead 20 of amplifier i4.

rEhe network comprises a follow up potenti- 2t, a rudder ratiopotentiometer 2l, a

potentiometer 24 has a resistor 25 which is connected across the ends ofa secondary wind ing ci transformer 3d. A slider 25 of potenti i eter isoperated over the surface of resistor 2S by a follow up connection 23extending from the servoinotor shaft l2. The potentiometer 2l a resistor2S which is connected across the slider 25 and a center tap 2! ofresistor 26. The potentiometer 21 includes an adjustable tap 29 whichmay be manually positioned over resistor 28 and which is connected tothe input lead i9 of amplifier l. Potentiometer 34 includes a resistor36 which is connected across the ends of secolidary winding 32 inparallel with resistor 26. Potentiometer 34 includes a slider 35 whichmay be manually adjusted over resistor 38 or may be operatedautomatically by a centering motor 38 to be described. Transformer 39includes a primary winding 3l Network 19 consists of a directional gyrorudder potentiometer lil having a resistor i2 and an adjustable slider43; a transformer i4 having a primary winding 9| and a secondary winding45; a rudder rate gyro potentiometer 48 having an adjustable slider 59;and a rate coordination potentiorneter i having a resistor 52 and anadjustable tap 53.

AInthe arrangement of network 49, resistor 92 of potentiometer di isconnected across the ends of secondary winding 5. A lead 5S extends fromslider i3 to slider 35 of the centering potentiometer 34. Slider i3 isadjusted by a directional gyro 51 to be described. Resistor 49 ofpotentiometer i3 is connected across the secondary winding '5 inparallel with resistor 42. Slider 50 of potentiometer 48 is operatedthrough an operative connection 5S extending from a rate gyro 69.Resistor 52 of potentiometer 5i has one end connected to a center tap 5eof resistor 49 and has its other end connected to slider 5U.

Network 62 consists of a vertical gyro rudder potentiometer 53 having aresistor 54 and an adjustable slider 55; a transformer having a primarywinding 3| and a secondary winding 68; and a turn control potentiometer'i0 having a resistor 'il and an adjustable slider T2. As arranged innetwork 62, the resistor 65 is connected across the ends of secondarywinding 68. A lead 59 extends from slider 65 of the vertical gyro rudderpotentiometer 53 to the slider 53 of the rate coordination potentiometer5|. The slider 65 is operated from vertical gyro 'I5 to be described.Resistor ll of the turn control potentiometer is connected across theends of secondary winding 68 in parallel with resistor 54. Lead lliextends from slider 'l2 to ground. Slider 'I2 is operated by a manuallyoperable turn control knob 76 through an operating connection 1l.

It will now be apparent that the networks are connected in electricalseries relationship in said control circuit. It is further apparent byreference to network 22 that the potential of center tap 2l of resistor29 is the same as that of the center coil of secondary winding 32. Ifwiper 25 be moved to the right of center tap 2|, the Voltage betweenslider 25 and center tap 2| varies with the magnitude of such movementand the phase of the voltage between the slider 25 and center tap 2l hasone phase with respect to the voltage across the secondary winding 32.If slider 25 be moved to the left of center tap 2l it is apparent thatthe voltage between the slider 25 and center tap 2! varies with themagnitude of such movement but the phase of such voltage is opposite tothe phase of the voltage obtained when slider 25 was moved to the rightof the center tap 2l. Voltag'es of variable phase and magnitude maytherefore be obtained by the movement of wiper 25 with respect to thecenter tap 2i. From the description of the operation of slider 25, it isalso evident how the sliders 35, 43, 59, 65 and 'E2 may be operated toprovide voltages which vary in phase and magnitude. Since the networksare vhorizontal axes.

4 connected in series a resultant voltage will be applied across theamplifier connections I9 and 29. The amplifier i4 will continue tooperate as long as there is a resultant signal in the input circuitthereto.

As stated previously the slider 43 is operated by a directional gyro 5l.This directional gyro may be of the conventional type having threeangular degrees of freedom. The directional gyro comprises an outervertical gimbal ring 89 whose trunnions 8| are suitably supported bybearings 82 in suitable supporting means. A rotor casing is trunnionedabout a horizontal axis Se in the outer gimbal ring 89. A rotor notshown is supported for rotation about a horizontal axis within casing 85at right angles to the axis 84. Suitable means (not shown) are providedfor rotating the rotor. The gyro 57 is so arranged in the aircraft thatupon movement of the aircraft about its vertical axis the gyro due "toits inherent stability will adjust the wiper Y@3 with respect toresistor 42 in proportion to the magnitude of the move-` ment of theaircraft and also in a direction dependent upon the direction ofmovement of the aircraft. A stop arrangement, now shown, may be providedto limit the amount of relative movement of the trunnions Bi withrespect to the bearings 82. A member 8S which extends from the left endof the casing provides a means for centering and locking the outergimbal Se with respect to its support bearings 82 in a manner to bedescribed.

Coacting with the member 86 to effect the centering or caging of thedirectional gyro 5'! is a caging mechanism 9i. Mechanism 9! includes ahollow cone-shaped member 8l whose inner surface may be moved intoengagement with member 85. rEhe cone-shaped member 3l is carried by aslidable armature 88. This armature 88 may be mounted for slidingrelation in any suitable means. The armature 88 coacts with a cagingcoil 92 and an uncaging coil 89.

The energization of the caging and uncaging coils 92, 89 is controlledby a caging relay 9&1. Relay 94 comprises an operating winding 95, awinding operated plunger 9S which operates a single-pole double-throwswitch arm 97, an out contact 99, and an in contact 98 between which theswitch arm is interposed. The winding of relay 94 is controlled by aswitch which may be operated from the turn control knob 16. This switchconsists of a switch arm lili] which is interposed between two spacecontacts IGI, 192 which are connected together.

The rate gyro 60 which through the operating connection 58 adjusts theslider 55 is of the type well known in the art having angular freedomabout two horizontal axes but which has its movement about one axisrestrained. An example of such type of rate gyro is disclosed as Tc inthe patent to Thiry, 2,190,390.

Reference is now made to Figure 1A. The vertical gyro 75 that operatesslider 55 of potentiometer 83 is of the electrically driven type havingthree degrees of movement about three axes. The gyro 75 is oftenreferred to as a horizon gyro or a flight gyro and has its rotor mountedin a casing for rotation about a vertical axis. The rotor casing inaddition is suitably supported for rotation about two respectivelyperpendicular The gyro may be of the type disclosed in application17,698, of John F.

,Schoeppel et al. The gyro 'l5 is provided with erecting means about thetwo horizontal axes for maintaining the gyro rotor vertical with respectto the earth. Such erecting means may beoftthe form Adisclosed in theaforesaidjapplicae tion of .Schoeppel et al.. The erecting means are:

indicated broadly at |04, |05 and are placed at right angles to one,another to indicate that they erect the rotor about the two respectivelyper- I The. erecting means pendicular horizontal axes. are controlled bya transformer |06 comprising a primary winding and two secondarywindings |09 and ||0. The erecting means |04 is connected to thesecondary winding ||0 through suitable means ||3, ||4. The erectingmeans is connected to the secondary winding |08 through suitable means||2. The gyro is so positioned in the aircraft that upon tilt of theaircraft about the roll axis the slider 65 will move along resistor 64.The rotor of vertical gyro 15 may be driven by a capacitor motor orother suitable driving means.

Various additional components of the appa.-P ratus whose function willbeclaried in a de,- scription of the operation thereof are alsoillustra-ted in Figure 1A. These components include an autopilot masterswitch which may be a single-pole single-throw knife switch comprisingswitch arm |21 and its coacting contact |22.

Switch |20 controls the energization of a power relay |23. The powerrelay comprisesk an operating coil |24, an. operable plunger |25, twosingle-throw switch arms |25, |21 and their respective contacts |23, and|29.

There are. provided two amplier relays and |3|. The first relay |30consists of an operating coil |32, a winding operated plunger |33, asingle-throw switch arml |34, and a contact with which arm |34 coacts.Thev second relay |3| consists of an operating coil |31, a windingoperated plunger |38, a single-throw switch arm |39, and a contact |48.The power relay |23 supplies D. C. voltage to the switch arms |34, |39of amplier relays |30, |3|. While the relays |30 and |3| of the ruddercontrol only have been illustrated, the automatic pilot ainplifier asdisclosed in the aforesaid application 447,989 includes a. pair ofrelays each for the elevator and aileron control' as well.

The relays I 30 and |3| control the direction of rotation of centeringmotor 35 and servomotor I3 through a rudder' engage relay |3. ativeparts' of relay I3 consist of an operating coil |4|, a winding operatedplunger |42, and four plunger operated arms |43, |44, andl |40. Theswitch arm |43 coacts with an out contact |48 and an in contact |41.coacts with. an out contact |50 and an in contact |49. The switch arm.|45 coacts with an out contact |52 and an in contact |5|. The

switch arm |40 coacts with an out contact |54' andan in contact |53.

The centering motor 38 may be of the permanent magnet type having ieldelements consisting of permanent magnets |58 and |51 andv operativeparts of the relay |38 consist of an operating winding |69, a windingoperated plunger |10, and single-throw switch arms |1|, |12 and |13.Thearms |1|, |12 and |13 are pivoted to a common bus bar |15. Switch armI1| coacts with a rudder engage relay in con- The switch arm |44' tact|161 Switch arm |12 coacts with an aileron' engage relay in contact |11.Switch arm |13 coactsr with an elevator engage relay in contact |18.

The circuit through the rudder engage relay winding |41v maybe broken bya normally closed rudder disengage switch comprising a contact bridgemember |8| and contacts |82 and |83 coacting with the bridge member. Theswitch |80 as stated is normally closed but may be temporarily opened.

The circuit through the winding |68 of the main engage relay |38 iscontrolled by several switch elements connected in series relation. Thisseries circuit includes firstly a main engage switch |86 consisting ofcontacts |81 and |88 and a bridge member |89 coacting therewith. Theswitch. |86 is ot the normally open momentarily closed type. Thiscircuit secondary includes an antiengage relay |90. consists o anoperating winding |9, a winding operated plunger |92, a plunger operatedswitch arm |93, and an out contact |04.

The, seriesr circuit thirdly includes a thermal delay switchA |95.Switch |05 consists or a heater element |95, a bimetal element |31, andan in Contact |98 with which the bimetal coacts.

This circuit fourthly includes a main disengage switch 200 comprisingtwo space contacts 20|, 202 with a member 203 coacting with thecontacts. The switch 200 is of the normally closed temporarily openedtype.

The circuit ifthly includes an C.-D. C. failure relay, The relay 205consists of an operating winding 203, a winding operated plunger 201,and. plunger operated` switch arms 208, 209. Switch arm 288 coacts withan in contact cli. Switch arm 209 coacts with an in contact 2|0.

This series circuit -inally includes the power relay |24 previouslydescribed.

The A. CHD. C. failure relay 205 also controls the circuit through thedriving motor for the rotor of vertical gyro 15. Ordinarily the circuitto the motor passes through a dropping resistor 2|4 which resistor isshunted by switch arm 208 'and in contact 2| on the operation of therelay 205.

The winding 206 of the failure relay 205 is controlled by a pilot relay2 |5. This pilot relay 2 l5 is located in the rectifier portion of theampli fier. The relay 2|5 consistsv of an operating winding 2|8, awinding operated plunger 2|?, a-

plunger operated switch arm 2|8, and an in con tact 2 9.

The `amplier of the aforesaid Gille applica-V tion discloses a rectifiersection which provides full wave rectification. For simplification ofdisv closure this rectier is illustrated herein as a. simple half-waverectiier 220. The rectifier 22.0 includes a single tube having a heaterelement 22 a cathode 222, and a plate or anode 223. The heater element22| is connected in series with other laments of tubes in the amplifierwhich other Ifilaments are indicated generally by resistor 225. Theoutput lead 224 of rectifier 220 is in parallel with the winding ZIB ofthe pilot relay 2 5 which winding becomes energized when the rectifierbecomes conducting.

The components of the apparatus illustrated in Figure 1A are associatedwith the rudder channel of the automatic pilot. However, it should beborne in mind that in addition to providing a pair of ampli-fieroperated relays similarr to relays |30 and |3| each for the aileron andelevator section, that the rudder engage re- The relay lay, thecentering motor, the servomotor, and the individual disconnect switchesare lalso duplicated for the aileron and elevator section of theA pilotwill be claried from a description of the operation below.

Operation The association of the automatic pilot with the controlsurfaces of an aircraft will become apparent by a consideration of theoperation. Suppose the pilot of the aircraft desires to ily by automaticpilot. To this end, the pilot initially closes the autopilot switch |23.D. C. voltage is thereby applied from a suitable source through lead230, switch arm 12|, contact |22, relay winding |24 to ground. The powerrelay |23 thus becomes energized and operates switch arms |23, and i2?.A. C. voltage which may be obtained from the ships supply is therebytransmitted from lead 232, contact |23, switch arm I2'I, lead 233, lead234, primary winding |38 of transformer to ground whereby the erectionmotor transformers are energized. |A. C. voltage is also applied fromthe energized lead 233, lead 235, bridge transformer primary winding3|'to ground whereby the bridge network secondary windings 32, 45, 63Figures 1A, are energized. Alternating voltage is valso applied fromenergized lead 233, lead 236, resistor 2I4, lead 237, to the drivingmotor for the vertical gyro rotor 15. A. C. voltage is also applied tothe portion ofthe Figure 1B ampli-Iier which controls they servomotorsand to the rectifier plate 223.

The operation of power relay |23 also supplies D. C. Voltage from asuitable source to lead 23i, contact |28, switch arm |23, to the main D.C. bus 233. D. C. voltage is thereupon applied to the ampliiier relayswitch arms |34 and 33. D. C. voltage is also applied from energized bus238, lead 239, switch arm 9?, contact 99, uncaging coil 39, to groundwhereby the caging mechlanism 3| is energized to uncage directional gyro51. D. C. voltage is also applied from energized bus 233, lead 240 tothe heater elements in the servomotor control section of the amplierrepresented by resistor 223, and to the heater element 22| of rectiiier223.

With the operation of the power relay |23, it is now evident thatalternating voltage is applied to the rotor motor of gyro vertical 'I3through a resistor 2| 4 whereby the voltage on the rotor motor is heldto below normal value. This reduction in the rotor motor voltageprevents the speed of the rotor from building up to a normal value andpermits the erecting means |04 and |05 of the vertical gyroscope 'i5 tomore quickly erect the rotor to the Vertical than if the rotor attainednormal speed. Were the speed of the rotor motor permitted to attainnormal value, the erection rate would be reduced. This initial rotationspeed is maintained approxi nately for about iifteen seconds to permitthe gyro rotor to approach erect position. This time interval iscontrolled by a time delay in the form of the pilot relay 2 i5 andrectiiier 223. After the rectifier heater element and cathode have beensufficiently warmed up and with anA. C. voltage on plate 223, therectifier becomes conducting following this interval and a circuit iscompleted through the operating winding 2|I5 of pilot relay 2|5. Thepilot relay 2| 5 thereby operates switch arm 2|8. Following operation ofthe pilot relay 2I5, av circuit is completed from 8.7. energized D.' 1C.bus 238, in' contact 2I9 of"relayi 2I5, switch arm 2I3, lead 24|, lead242, operating" winding 206 of the A. C.-D. C. failure relay to ground.A circuit is concomitantly completed` from energized lead 24|, lead 243,to heater element |33 of the thermal delay switch |95, andv to ground.

IThe operation of the A. C.D. C. failure relay 235 applies fullalternating voltage to the rotor motor of gyro vertical 'I5 throughenergized lead 236, switch arm 203, in contact 2II, lead 244, lead 231,to the rotor driving motor of gyro Vertical 75. The rotor motor is nowpermitted to attain its normal-operating speed.

lThe operation of the A. C.D. C. failure relay 205 also extends D. C.voltage from energized bus 233, lead 244, switch arm 203, contact 2|3,lead 245, the closed main disengage switch 200, lead 246, lead 247, tothe in contact |98 of the still unoperated thermal delay switch |95.-

Concomitantly the operation of the A. C.-D. C. failure relay 203 causesa circuit to be 'extended from energized lead 243, main disengage switch203, lead 243, switch larrn |43, out contact |48, lead 249, coil 35 ofthe caging relay 94 to ground. The operation of the caging relay 34completes a circuit from energized bus 238, lead 233, switch arm 37, incontact 33, caging coil 33 of the caging mechanism 9| to ground. Theoperation of the caging mechanism 9| centers andv locks the directionalgyro in center po sition.

Following a short time delay period during which it is anticipated amongother things that the motor which drives the rotor of gyro 'i5 hasapproached its normal speed, the thermal delay switch which has had itsheater |93 energized operates. A circuit is now completed from theenergized lead 247, thermal delay switch |35, to lead 250. Y

Concurrently with the operation of the pilot relay 2I5 in the rectifiersection, the rectier will have also provided control voltage to theservom-otor control section of the ampliiier through lead 224 as furtherdisclosed in application 447,989.

Should the rudder control bridge of Figure 1B be in unbalanced conditionat this time, the amplifier I4 will operate. One or the other of relaysI30, I3| will be operated at this time depending upon the direction ofunbalance of the amplier control circuit. If the direction of unbalancecause the operation of amplifier relay |30, a circuit extended fromenergized switch arm |34, contact |35, switch arm |46, contact |34, anda parallel circuit through armature |58 and resistor |30 of centeringmotor 33, lead 252, antiengage relay coil |9I, to ground. rIhe operationof centering motor 38 tends to rebalance the input circuit of amplierI4. It is apparent that if the direction of unbalance initially were inthe opposite direction, that the relay I3I would be operated so that thecentering motor 38 would rotate in an opposite direction to rebalancethe input circuit of ampliiier I4. As long as the centering motorrotates which is apparently as long as the input circuit of amplifier i4is unbalanced, the antiengage relay winding |9i will be energized. Afterthe input circuit is balanced, the Winding |9I of antiengage relay |93is no longer energized and the relay falls to the out position. Acircuit is extended from energized lead 250, switch arm |93, contact|94, through indicating light 228 to ground.

The energization of indicator light 228 as-A g. sures the pilot that hemay now engage or condition the control surfaces for operation by theservomotors. The pilot may thus operate main engage switch |86 bymomentarily depressing bridge member |59. A circuit is thus completedfrom energized lead 25S, main engage switch |85, lead 254, winding |55of the main engage relay |68, to ground.

The operation of the main engage relay |68 extends D. C. Voltage fromenergized lead 24S, bus bar |15, switch arm ITI, contact |16, lead 255,winding |4I of the rudder engage relay I6, rudder disconnect switch |80,to ground.

The operation of the rudder 'engage relay I6 provides it with a holdingcircuit extending from energized lead 24S, switch arm |43, holdingcontact I4?, winding |4I, rudder disengage switch |80 to ground.Concornitantly the aileron and elevator engage relays are operated andprovide their own similar holding circuits as is provided by the rudderengage relay.

The operation of the switch arm |43 of the rudder engage relay breaksthe circuit to the caging relay coil and relay 94 assumes the outposition. The switch arm 91 of the caging relay 54 is now in abutmentwith contact 99 whereby the uncage coil 89 is energized to uncage thedirectional gyro yEil.

The operation of switch arm |44 of the rudder engage relay e'nergizesthe brake operating solenoids |52 and |53 of servomotor I3 to conditionthe association of the servomotor and control surface whereby thecontrol surface assumes a braked condition. The operation of switch arms|45 and |46 in the rudder engage relay associates the amplifier' relays|30 and |3| with the servomotor clutch operating coils |64 and |65respectively. The centering motor 38 is no longer controlled by theamplifier relays when the rudder engage relay is operated. In a similarmanner the elevator and aileron engage relays will have energized theirservomotor Ybrake solenoids and will have transferred the amplifierrelays control effect from their respective centering motors to theirrespective servomotor clutch coils.

The servomotors are now conditioned for operation by their respectiveamplifier relays and the aircraft will be stabilized in the attitudeassumed when the main engage switch |86 had been operated.

It is evident that the sequence of operation described willautomatically take place even though the pilot should ride the mainengage switch |86. The term ride infers that the pilot has operated themain engage switch at the same time that he has operated the autopilotswitch |20. By riding the main engage switch it is evident that thepilot will engage the automatic pilot in the shortest possible timeconsonant with the proper conditioning of the apparatus.

With applicants rectifier operated switch and should there be a failureof alternating voltage on the system, it is evident that while theaircraft would not be stabilized by the attitude responsive g-yroscopesyet the servomotors and control surfaces are automatically disassociatedfor subsequent manual control surface operation. Such disassociation ofservomotor and control surface is desirable to permit manual operationof the control surface during the emergency resulting from failure ofthe bridge signal supply voltage without having to overpower theservomotor brakes.

Upon failure of the alternating voltage supply or the directvoltagesupply in applicants arrangement the rectier tube in rectier 220no longer is conducting and the pilot relay 2 I5 is deenergized. Theopening of the pilot relay 2|5 deenergizes the A. C.D. C. failure relay205 which opens the holding circuit for the rudder engage relay winding|4I. The deenergization of the coil |4| of the rudder engage relaytherefore results from either an alternating or direct voltage failureand opens the brake coil circuits to disassociate the servomotor fromthe control surface. Concomitantly the indicator light 228 is no longerenergized thereby indicating to the pilot that he should assume manualdirect operation of the control surfaces. Automatic disengagement of`the autopilot and indication thereof is thus provided on failure ofeither supply voltage.

In order to subsequently engage the automatic pilot with the controlsurfaces after power failure, it will be apparent that the centeringmotors must again first balance the various control circuits to theirrespective amplifiers before the antie'ngage relay will be unoperatedconsequently no residual signal which may have arisen after powerfailure will remain in the respective bridge circuits to cause a lurchin the aircraft upon the subsequent operation of the main engage swit'ch|85.

Should the pilot desire to control the aircraft 'through the automaticpilot while it is so engaged, with the control surfaces, he may operatethe manual turn control I6 in one direction or the other depending onthe direction of turn de sired. The operation of the turn control knob.e causes the switch arm |00 to engage one or the other of spacedcontacts |0I, |02 from energized lead 246, lead 260, relay coil windingto ground. The operation of the relay 94 results in the caging of thedirectional gyro 51 as stated. The adjustment of the return control knob'I6 causes the movement of slider 12 with respect to resistor 1I toprovide a control signal in the input circuit of amplier I4 and in theaileron amplier input circuit in a manner well known to those skilled inthe art whereby manual turn of the aircraft is provided.

It is now evident that this invention provides a novel interlock ormonitoring arrangement for an automatic pilot wherein rapid initialerection rate for the vertical flight gyro is available at reduced rotorspeed and where the gyro rotor is subsequently permitted to approachnormal speed and thus maximum rigidity before such gyroscope is utilizedas a stabilizing element for an aircraft. Vlhnther, that on failure ofthe alternating voltage or the direct current voltage supply, theautomatic pilot is automatically disa'ssociated from the controlsurfaces and an indication is provided to this effect so that manualcontrol may be initiated without it being necessary for the pilot toovercome the servomotor braking action; and when subsequent automaticcontrol is to be initiated, proper' safeguards become operative toprevent lurching of the aircraft.

While my invention has been disclosed in a preferred embodiment, it isapparent that various changes and arrangements thereof may be provided.I therefore do not wish my invention to be limited to the preciseembodiment but only as circumscribed by the following claims.

I claim as my invention:

l. Control apparatus for an aircraft having a control surface forcontrolling 'the attitude of said aircraft about an axis,.said apparatuscomlascisse-1 prising: a power means which may be operatively associatedwith said control surface; control means for said power means includinga balanceable system having control devices for affecting its balance;means including a gyro having erecting means and responsive to movementJabout an axis for operating one control device; follow up means fromsaid power means to another device; means for initiating rotation ofsaid gyro rotor at less than normal operating speed and for energizing afirst time delay device; means operated by said first time delay devicefor applying full energy to said gyro rotor and to a second time delaydevice, and means controlled by said second time delay device forassociating said power means with said control surface, whereby saidgyro has reached operating conditions before it controls said powermeans.

2. Control apparatus for an aircraft having a control surface, saidapparatus comprising: power means operatively disengageably connectedwith said control surface; a control means for said power meansincluding an amplier having a rectifier for controlling the operation ofsaid amplifier; relay means operated in response to conduction by saidrectifier; means for connecting said rectifier to a source ofalternating voltage; means responsive to tilt about an axis for alsoeffecting operation of said amplifier; and means controlled by saidrelay means for causing said power means to be operatively engaged withsaid control surface.

3. Control apparatus for an aircraft having a control surface, saidapparatus comprising: power means normally unoperably connected withsaid control surface; a control means for said power means including anamplifier having a rectifier for controlling the operation of saidampliiier; relay means operated in response to conduction by saidrectifier; means for connecting said rectifier to a source ofalternating voltage; means responsive to tilt about an axis for alsocontrolling operation of said amplifier; said responsive meanscomprising a gyroscope having a rotor energized with other than normalvoltage upon operation of said connecting means; a time delay connectingmeans; means operated by said relay means for applying full voltage tosaid gyro rotor and for energizing said time delay means; and meanscontrolled by said time delay means for operably connecting said powermeans with said control surface.

4. Control apparatus for a craft having a controlsurface, said apparatuscomprising: power means operably disengageably connected with saidcontrol surface; control means for said power means said control meansbeing normally disconnected from with power means, said control meansfurther including an amplifier having a rectifier for controlling powerto said amplifier; a balanceable control circuit for said amplifier;means for unbalancing said control circuit; relay means operative uponconduction of said rectifier; and additional means controlled by saidrelay means for momentarily connecting said power means with saidcontrol means and with said control surface; and means responsive tooperation of said additional means and continued operation of said relaymeans for maintaining said connection.

5. Control apparatus for a craft having a control surface, saidapparatus comprising: power means normally unoperably connected withsaid control surface; control means for said power means said controlmeans being normallyl disconnected from said power means, said controlmeans further including an amplifier having a rectifier for controllingpower to said amplifier; a balanceable control circuit for saidamplifier; means for unbalancing said control circuit; means forrebalancing said control circuit while said control means and powermeans are disconnected; relay means operative upon conduction of saidrectifier; an additional means controlled by said relay means formomentarily connecting said power means with said control means and withsaid control surface; and means responsive to operation of saidadditional means and continued operation of said relay means formaintaining said connection.

6. `Control apparatus for a dirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement of said craft; means for operating said power means butnormally disconnected therefrom, said control means including abalanceable system; a gyroscope having erecting means and responsive totilt about an axis for unbalancing said system, motor means controlledby said operating means while said power means is disconnected therefromfor rebalancing said system, means for connecting said gyroscope rotorto a source of power whereby said rotor is rotated initially at lessthan normal speed and for initiating operation of a first time delaymeans; means operated by said first time delay device for applying fullpower to said rotor so that it may attain maximum speed and forinitiating operation of a second time delay device; and means operatedby said second time delay device for connecting said operating meanswith said power means and for conditioning said power means.

'7. Control apparatus for a dirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement of said craft; means for operating said power means butnormally disconnected therefrom, said control means including abalanceable system; a gyroscope having erecting means and responsive totilt about an axis for unbalancing said system, motor means controlledby said operating means while said power means is disconnected therefromfor rebalancing said system, means for connecting said gyroscope rotorto a source of power whereby said rotor isrotated initially at less thannormal speed and for initiating operation of a first time delay means;means operated by said first time delay device for applying full powerto said rotor so that it may attain maximum speed and for initiatingoperation of a second time delay device; further means for connectingsaid operating means with said power means and for conditioning saidpower means; and circuit means for controlling operation of said furthermeans including said second time delay device and means responsive tocontinued operation of said motor means.

8. Control apparatus comprising, a gyroscope provided with erectingmeans for its rotor; means for energizing said erecting means, forconcomitantly connecting said rotor to a source of power whereby saidrotor may rotate at other than normal speed, and for initiatingoperation of a first time delay device; means operated by said firsttime delay device for connecting said rotor to said source of power sothat said rotor may rotate at normal speed and for initiating operationof a 'second time delay device; a controlled device and means operatedby said second and said controlled device. l

9. Control apparatus comprising: a vertica 'gyroscope having erectingmeans; a directional gyroscope; caging means for said directionalgyroscope for centering said gyroscope rotor with respect to itssupport; means for connecting said vertical gyroscope rotor with asource of power whereby said rotor may be rotated at other than itsnormal speed, for concomitantly energizing its erecting means, andinitiating operation of a first time delay device; additional meansincluding means operated by'said first time delay device for connectingsaid vertical gyroscop'e rotor to said source of power whereby saidrotor may rotate at normalspeed, for initiating op eration of a secondtime delay device, and for oaging said directional gyroscope rotor; andfurther means including means operated by said second time delayv devicevrectional lgyroscope rotor.

10. Control-apparatus for a vdirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement ofV said craft; means for operating said power means; means forcontrollng said operating means including a gyroscope responsive to tiltabout an axis and having erecting means; means for initially applyingless than full voltage to said gyro rotor rotating means; a iirst timedelay device energized concomitantly with said gyro rotor rotatingmeans; means operated by said first time delay device for applying fullvoltage to said rotor rotating means and for energizing a second timedelay device; and means controlled by said second time delay device foreffecting the conditioning of said power means.

1l. Control apparatus for a dirigible cra-ft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement of said craft; means for operating said power means; means forcontrollng said operating means including a gyroscope responsive to tiltabout an axis and having erecting means; means for initially applyingless than full voltage to said gyro rotor rotating means; a first timedelay device energized concomitantly with said gyro rotor rotatingmeans; means perated by said first time delay device for applying fullvoltage to said rotor rotating means and for energizing a second timedelay device; manually operable means effective upon operation of saidsecond time delay means for effecting the conditioning or. said powermeans; and means for maintaining said condition despite release of saidmanual means but upon continued operation of said first time delaydevice.

12. Control apparatus for a dirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement of said craft; means for operating said power means whenconditioned including a controller operable from a normal position;means including a gyroscope responsive to a movement of said craft aboutan axis for operating said controller; means for conditioning said powermeans to change craft direction upon operation of said power means;means for caging and uncaging said gyroscope means, a time delay device,means for energizing the time delay device to effect an operationthereof and for concomitantly operating said caging mechanism to uncageposition, means effective upon operation of said time delay device andto nonoperation of said conditioning means for said power for uncagingsaid di- 14 means for operating said mechanism to cage position, andmeans for operating said conditioning means and for simultaneouslymoving said mechanism to uncage position.

13. Control apparatus comprising: a vertical gyrosoope of theelectrically driven type having erecting means; a directional gyroscope;caging means for said directional gyroscope for centering said gyroscoperotor with respect to its support;

means including a resistor for connecting said 'lay means operated bysaid first time delay device an operation thereof for shunting saidresistor and connecting said vertical gyroscope rotor directly to saidsource of power` whereby said rotor may rotate at normal speed, forinitiating operation of a second time delay device, and for caging saiddirectional gyroscope rotor; and means in cluding a manually operableswitch and a relay operated by said second time delay device foruncaging said directional gyroscope` rotor; indicate ing means operatedby said second time delay device; power means; operable control meansfor said power means including a plurality of operation initiatingdevices; means for operating one initiating device by said verticalgyroscope; and means for operating a second initiating device by saiddirectional gyroscope.

14. Control apparatus for a dirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling on subsequentoperation thereof the direction of movement of said craft; an amplier,having two control circuit terminals and two power input terminals, forreversibly operating said power means depending on the phase relation ofthe voltage across said pairs of terminals; electronic rectiiier means;a control circuit for said amplifier connected to said control circuitterminals; means for energizing said input terminals, said controlcircuit, and said rectifier plate from a source of alternating voltage;additional means including means energized by conduction of saidrectifier means and a manually operable switch for conditioning saidpower means, and means responsive to change in direction of movement ofsaid craft for setting up a control signal in said control circuit.

l5. Control apparatus for an aircraft comprising: power means which isnormally unoperably connected with a control surface of the aircraft;control means for operating said power means; gyroscope means foroperating said control means; means including a thermionic tube; meansfor energizing rotation means for the gyroscope rotor at less than fullvalue and for energizing said thermionic tube; means operated onconduction of said thermionic tube for fully energizing said rotorrotation means; means including a thermal responsive switch energized onconduction of said thermionic tube; and means including` meanscontrolled by said thermal responsive switch for opel-ably connectingsaid power means with said control surface.

16. Control apparatus for a dirigible craft, said apparatus comprising:power means adapted to be conditioned for controlling the direction ofmovement of said craft; means for operating said power means; means forcontrolling said operating means including a gyroscope responsive totilt about an axis and having erecting means; means for initiallyapplying less than full volt/age to said gyro rotor rotating means; arst time delay device energized concomitantly with said gyro rotorrotating means; means operated by said iirst time delay device forapplying full Voltage to said rotor rotating means and for energizing asecond time delay device; manually operable means eective upon operationof said second time delay means for effecting the conditioning of saidpower means; means for maintaining the conditioning of said power means;and means responsive to unoperation of said iirst time delay device forrendering said maintaining means ineiiective.

17. Control apparatus for a craft having a control surface, saidapparatus comprising: power means normally disengageably connected withsaid control surface; control means for said power means said controlmeans being adapted to be connected with said power means, said controlmeans further including an amplier having a rectifier for controllingpower to said amplifier; a balanceable control circuit for saidampliiier; means for unbalancing sai-d control circuit; means forrebalancing said control circuit while said control means and powermeans are disconnected; relay means operative upon conduction oi saidREFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,896,805 Sperry et al. Feb. 7,1933 2,344,126 Carlson Mar. 14, 1944 2,429,605 Brannin Oct. 28, 19472,464,629 Young Mar. 15, 1949 FOREIGN PATENTS Number Country Date102,197 Sweden July 29, 1941 820,614 France Nov. 16, 1937

